Flexible pipeline joints

ABSTRACT

A flexible length of pipe is formed from at least two pipe sections joined by a flexible element such as a closed toroidal shell or open convoluted forms.

This is a division of application Ser. No. 163,557, filed June 27, 1980,now Pat. No. 4,421,345.

BACKGROUND OF THE INVENTION

Two pipe ends can be joined easily when the pipes are very flexible inbending. Some pipe materials are more flexible than others, e.g., rubberhoses are more flexible than steel pipe, and small diameter pipes aremore flexible than larger diameter pipes. Generally, for a givenmaterial, the flexibility of the pipe is proportional to the cube of thediameter of the pipe.

Large pipes, for example 18-60 inches in diameter, are so stiff thatfield bends usually are not feasible, and bends are made in these pipesin special plants designed for this purpose. In the case of submarinepipeline joints made on-bottom, it is difficult to both manipulate andalign the ends of large diameter pipes for joining because such pipesare stiff axially as well in bending. Remote control operations andhandling of massive equipment from surface vessels also addsubstantially to the difficulties of these problems.

Accordingly, the present invention provides a new and useful flexibleelement which substantially alleviates or overcomes the above notedproblems of the prior art and provides further advantages as will bemore apparent hereinafter.

SUMMARY OF THE INVENTION

The present invention pertains to a flexible element useful for joiningpipelines, which element can be used to make a length of pipe moreflexible axially, as well as in bending. The flexible element can beused in submarine pipelaying (where pipe alignment is difficult) to addflexibility to the line at discrete locations along the length thereof.This would assist, for example, in joining two strings of pipe togetherby welding or by using mechanical connectors. One specific use is inbringing two flanges together. If there is a rotational (bending)misalignment between the flanges, the flexible element can make iteasier to achieve the required rotation thereby permitting clamping ofthe flanges. If there is an axial gap between flanges, the flexibleelement can reduce the force required to close this gap.

More specifically, the present invention pertains to a flexible lengthof pipe composed of at least two pipe sections joined by a flexibleelement disposed between the ends of the two pipe sections. The flexibleelement may have somewhat open configurations such as that of a toroidwith a semi-circular cross section or other forms of a cylindrical shellwith at least one convolution around the circumference welded to thepipe ends to form a pressure-tight joint. The flexible element can thusbe thought of as a ring-like section approximating a short joint ofpipe, welded between two pipe ends. If the flexible element (ring) were,in fact, a short joint of pipe it would be no more flexible than thepipe. If the ring cross section is curved or convoluted, then the ringbecomes more flexible in the pipe axis direction. This is because theelement flexes in bending in addition to stretching. And, the bendingflexure is much greater than strenching alone. Also, the flexible ringelement may have an open-sided rectangular cross section and join thepipe sections so that the innermost parts of the ring connect with thepipe ends. A solid insert such as a solid ring or other inserts whichare lined up like a ring may be utilized adjacent to the convolutions(inside or outside of the flexible element) to prevent the deformationof the element beyond a prescribed amount. Other features of theinvention will be apparent from the following description.

DESCRIPTION OF THE DRAWING

FIG. 1 shows a profile of two pipe ends connected by a circular toroidalelement. The reduced pipe diameter of this basic concept makes it lesspreferred than some of the embodiments following.

FIG. 2 depicts an exaggerated deformation of the toroidal element due tobending moment in the pipe.

FIG. 3 shows a toroid made of larger mean diameter so that its minimumdiameter is at least equal to the pipe inside diameter.

FIG. 4 discloses other more preferred forms of the flexible element suchas a semi-circular shape in FIG. 4(a) and a straight line version ofFIG. 4(b).

FIG. 5 shows a version of the element using a wide interior shell-likering with ridges on each end to limit deformations.

FIG. 6 provides an embodiment wherein flexible elements are incorporatedas part of a three-point bending frame.

DESCRIPTION OF PREFERRED EMBODIMENTS

The present invention pertains to a flexible element for joiningpipelines, useful for making a length of pipe more flexible axially aswell as in bending, depending upon the exact design of the pipeline. Itis useful particularly in submarine pipelaying to add flexibility to theline at discrete locations along the length thereof to assist, forinstance, in the joining of two strings of pipe together by mechanicalconnectors or by welding. It also can be used to bring flanges together,or in the event that there is a rotational misalignment, the element canmake it easier to achieve rotation to permit clamping of the pipes.Similarly, if there is an axial gap between flanges, a flexible elementreduces the force required to close the gap. In addition, anotherapplication of the flexible element of the invention is to compensatefor thermal effects on pipelines, thereby acting as an axial contractionor expansion joint. Internal inserts and/or external and internal clampscan be used to limit the rotation and axial elongation occurring.

Referring to the drawings, FIG. 1 provides a profile of two pipe endsconnected by a circular toroidal element of diameter equal to that ofthe pipe. Thus, toroid is placed between pipe end 2 and pipe end 3. Asolid insert 4 is placed inside the toroid 1. Such inserts, frequentlysolid rod segments, limit the deformation of the toroid produced byaxial or bending loads in the pipe.

Exaggerated deformation of the toroidal flexible element 1 is shown inFIG. 2. This deformation is due to a bending moment in the pipeline.Inserts 4 stop the ovalling of the toroid once the prescribed amountoccurs. The inserts preclude buckling of the toroid and produce astiffness condition similar to that of a bent pipe without a flexibleelement. In a similar manner, a toroidal flexible element can be used toflex due to axial loads. Of course, flexing may be due to the combinedeffects of axial and bending loads as well.

In normal pipeline operations, it frequently is desirable to pass acleaning ball or cylindrical "pig" through the line without obstruction.For this operation to be effected with the present invention, the toroidmust be of larger mean diameter so that its minimum diameter is at leastequal to the pipe diameter. The eccentric toroid of FIG. 3 accomplishesthis purpose. It will be noted that pipeline 30 has a bell shaped end 31which allows the toroidal element 1 and insert 4 to be placed outside ofthe diameter of the pipe which, of course, allows pigs or other cleaningelements to be passed through the pipe without obstruction.

Insert 4 can be a ring-shaped rod or a thick-walled pipe. Alternatively,the insert can be multiple straight rod or pipe elements, of shortenough lengths to minimize curvature effects, or even multiple balls. Ifit is desired to prevent axial deformation while permitting bendingdeformation in a predetermined plane, the multiple balls, rods, pipes,etc. may be of varying diameters. In yet another embodiment, apreviously flexed joint can be rigidized by filling the flexible toroidwith a grouting medium such as epoxy or concrete.

Buckling or deformation of the toroid can also be controlled by fluidfilling and/or by pre-pressurization. If, however, rigid inserts areused, the toroid can be vented to the inside of the pipe or to theoutside of the pipe, depending on the ratio of internal and externalpressures, in order to minimize principal stresses and thus minimizefatigue damage due to fluctuations in internal pressure.

FIGS. 4(a) and 4(b) show other more flexible and potentially more usefulversions of the flexible element other than the eccentric toroid of FIG.3, which may be employed in order to permit passing of a pig or cleaningball through a pipeline. In FIG. 4(a) the flexible element 40 has asemi-circular convoluted shape and the insert 41 has a shape similar tothat of the toroid. The diameter of pipeline 42 is thus the same as theminimum diameter of the semi-circular shape and insert. An alternativeembodiment is shown in FIG. 4(b) which employs a flexible element havinga flat-sided rectangular cross section 43 and has a solid insert ring 44which is similar in shape to the rectangular flexible element.

FIG. 5 shows a version of the flexible element using a wide internalretaining ring 50 instead of the narrow inserts previously described.Ring 50 has ridged ends which fit into grooves 51 and 52 inside the pipeon both sides of the flexible element 53. Thus, the ring replacespreviously dedcribed inserts which would not be effective in tension.External mechanical ring clamps, not shown, fitting around and outsidethe convolution or convolutions may be employed to limit deformations.

Flexible elements as shown in the above described figures can also beincorporated as part of a three point bending frame as shown in FIG. 6so that bending energy can be applied to achieve rotation. Thedistortion can be limited and then locked in by the loading means. Pipe60 extends through three point frame 61, and flex element 62 is held inplace by loading means 63 such as a pair of hydraulic jacks. The jackscan be self-locking or otherwise locked to prevent subsequent movementsof the joint.

The flexible elements or convolutions of the present invention can beutilized in series, using any of the previously described variations inorder to solve any problem connected with laying pipelines in the eventthat a single flexible element is insufficient to produce the requiredbending or axial flexing of the line. Other combinations of the abovedescribed elements will be evident to those skilled in the art withoutexercise of invention beyond that above described.

What is claimed:
 1. A flexible length of pipe comprising at least twopipe ends flexibly joined with a flexible metallic element which iscircumferentially outwardly extending and concave to the interior of thepipe and an interior retaining widering sleeve having ridges at its endsto fit into circumferential grooves on the interior surface of the pipesections on both sides of the flexible element which separates theinterior of the flexible element from the interior of the pipe, theinside surface of the retaining sleeve being essentially flush with theinside surfaces of the pipe sections.